Utilization of motion and spatial identification in mobile RFID interrogator

ABSTRACT

A system and method of using motion or spatial identification technology with a mobile RFID reader to detect whether an RFID tag is part of a forklift load or other ambulatory space includes determining if a tag is within a defined space or if a tag is in motion relative to a mobile RFID reader. The system and method determines whether a particular RFID tag is part of a forklift load/space, has been added to or removed, is an extraneous tag, etc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/028,626, entitled “UTILIZATION OF MOTION AND SPATIAL IDENTIFICATIONIN MOBILE RFID INTERROGATOR”, filed Feb. 14, 2008, and is herebyincorporated by reference.

BACKGROUND

Forklift-mounted and other types of mobile RFID systems encounterdifficulties in determining which tagged items are loaded and which arenot. Under certain conditions RFID readers may read tags which are faraway as legitimately loaded items. Extraneous tag reads like these aredifficult to filter out using current technology and introducesignificant inaccuracies into the system.

Typically, software filtering based upon pick lists and hysteresis hasbeen used to eliminate the detection of extraneous tags. However, thesoftware involves modification to the application or the backend systemthat requires the data.

Complex antenna schemes which only allow tags within a well-definedspace of the forklift load area to be read have been used. However,these systems tend to be unreliable and expensive to produce andinstall.

There is a need for a system that overcomes the above problems, as wellas providing additional benefits. Overall, the above examples of somerelated systems and associated limitations are intended to beillustrative and not exclusive. Other limitations of existing or priorsystems will become apparent to those of skill in the art upon readingthe following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating an example of a method ofdetermining which RFID-tagged packages are on a forklift using a volumesensor.

FIG. 2 is a flow chart illustrating an example of a method ofdetermining which RFID-tagged packages are on a forklift using a motionsensor.

FIGS. 3A and 3B show a flow chart illustrating an example of a method ofdetermining the motion of an RFID tag by measuring the change of thephase angle of the tag response.

FIG. 4 shows phase angle measurements taken of three stationary tags(top graph) and one tag moved discrete distances (bottom graph).

FIG. 5 shows variations in phase angle between measurements taken at thebeginning of a tag response and measurements taken at the end of a tagresponse for stationary tags (top graph) and a tag moved discretedistances (bottom graph).

FIG. 6 shows the received signal strength indication measurements for atag moved discrete distances.

FIG. 7 shows a graph of measured phase angle difference as a function ofreceived signal strength indication measurements.

FIG. 8 shows a block diagram of an example RFID reader system.

FIG. 9 shows another block diagram of an example RFID reader system.

FIG. 10 shows a block diagram of an example mobile computer that can beused with an RFID reader to determine which RFID-tagged packages are ona forklift.

FIGS. 11A and 11B show measured accelerometer data and derived velocityand position data.

DETAILED DESCRIPTION

Described in detail below is a method and system of using motion and/orspatial identification technology to determine if a mobile RFID readeris in motion and also to determine whether a particular RFID tag is partof a forklift load, has been added to or removed from the forklift load,or is an extraneous tag.

Various aspects of the invention will now be described. The followingdescription provides specific details for a thorough understanding andenabling description of these examples. One skilled in the art willunderstand, however, that the invention may be practiced without many ofthese details. Additionally, some well-known structures or functions maynot be shown or described in detail, so as to avoid unnecessarilyobscuring the relevant description.

The terminology used in the description presented below is intended tobe interpreted in its broadest reasonable manner, even though it isbeing used in conjunction with a detailed description of certainspecific examples of the invention. Certain terms may even be emphasizedbelow; however, any terminology intended to be interpreted in anyrestricted manner will be overtly and specifically defined as such inthis Detailed Description section.

It would be useful to know the location of RFID-tagged packages inplaces like warehouses or distribution centers where there are a largenumber of tagged packages. In addition, the packages may be moved fromone location to another, for example, to complete orders or to placepackages into an order processing queue. Forklifts may be used to movelarge quantities of tagged packages. An RFID reader, whether mobile orstationary, may under certain conditions erroneously read and identifyan extraneous tag as part of the forklift load when the tag is actuallylocated on a shelf or elsewhere in the warehouse. Thus, there is a needfor a system that can reliably provide information, for example to aforklift operator or to a database, as to what is being carried on aparticular forklift load.

Spatial identification technology (SID) may be used to define a space infront of a forklift as a “load space,” where the load space may beeither a certain volume or area in front of the forklift. Packageswithin that volume or area in front of the forklift are considered onthe load, while packages outside of that area are considered not on theload. SID may also be used to detect when a tagged item is in motion anda tagged item's proximity to the reader antenna. SID may include, but isnot limited to, traditional motion sensors using infrared light or lasertechnology, vibration sensors, gyroscopes, and accelerometers. SID maybe built into an RFID reader system or alternatively be a separatesystem or sensor (e.g., be built within a vehicle).

The following three published documents discuss SID in greater detailand are incorporated by reference: (1) U.S. Pat. No. 6,600,443,entitled, “Method and Apparatus to Determine the Direction to aTransponder in a Modulated Backscatter Communication System”, filed Oct.18, 2002; (2) U.S. Pat. No. 6,476,756, entitled, “Method and Apparatusto Determine the Direction to a Transponder in a Modulated BackscatterCommunication System”, filed Jun. 4, 2001; and (3) PCT Publication No.WO 2007/035833, entitled, “Method, Apparatus, and System for Selectingand Locating Objects Having Radio Frequency Identification (RFID) Tags.

FIG. 1 illustrates an example volume sensor detection process 100 thatuses a volume sensor with a forklift-mounted RFID reader for detectingextraneous tags and determining which RFID-tagged packages are on aforklift. At block 110, the limits of a load space, such as the volumeof space in front of and on a forklift, are defined. For example, thepositional data of the corners of the selected load space are determinedand stored for use by the RFID reader. Positional data may comprisedistance from and angle with respect to the mounted RFID reader.Alternatively, dimensions of the load space can be entered into thedatabase together with a reference point on the forklift for definingthe load space, such as the mounted RFID reader. At block 120, usingSID, an RFID tag potentially located in the load space is read by anRFID reader on the forklift.

At decision point 130, it is determined whether the tag read by the RFIDreader is within the load space defined at block 110 by using aSID-based volume sensor. For example, the distance from and angle withrespect to the mounted RFID reader of the RFID tag are determined andcompared to the positional data of the corners of the defined loadspace. The distance between the RFID tag and the RFID reader may bedetermined in many ways. For example, the RFID reader may contain logicfor determining the distance based upon the received signal strength.Alternatively, the RFID reader may include two or more antennas thathave known separations. Based upon the signal strength received at eachof the antennas and the lag time between detecting an RFID tag'spresence at each antenna, the system may triangulate the location of theRFID tag to give higher resolution as to the proximity of the RFID tagfrom the reader. The angle of the RFID tag with respect to the RFIDreader may be determined as described in the above referencedpublications.

If at decision point 130, it is determined (block 130—Yes) that the tagis within the load space of the forklift, at block 140, the tag, andthus the package to which the tag is attached, is considered part of theforklift load. At block 160, the determination that the tag isconsidered part of the load is stored in a database for use by the RFIDsystem in routing tagged packages. The process continues in the samemanner with other RFID tags by returning to block 110. Because thelimits of the forklift load space may change due to movement of theforklift, at block 110, the limits of the forklift load space arere-defined for use in determining whether the next RFID tag is part ofthe load or not.

If at decision point 130 it is determined (block 130—No) that the tag isnot within the load space of the forklift load, at block 150, the tagand its corresponding package are not considered part of the forkliftload. At block 160, the determination that the tag is not consideredpart of the load can be stored in a database for use by the RFID systemin routing tagged packages. The particular RFID tag may be an extraneoustag identified by the RFID reader due to RF reflections or other RFnoise in the warehouse environment and may be safely excluded from theforklift load. The process continues in the same manner by returning toblock 110 to re-define the limits of the forklift load space for use indetermining whether the next RFID tag is part of the load or not.

FIG. 2 illustrates an example motion sensor detection process 200 thatuses a motion sensor for detecting extraneous tags and determining whichRFID-tagged packages are on a forklift.

At block 205, a motion sensor detects motion of an RFID reader mountedon, for example, a mobile forklift. Possible ways of detecting motion ofa forklift include, but are not limited to, taking an electrical signalon the forklift (e.g. from its speedometer) which indicates it is inmotion and feeding the signal into the RFID reader either through ageneral purpose input/output terminal or a dedicated input; using atraditional motion sensor based upon infrared light, laser light, orvibration, a gyroscope, an accelerometer, etc. and feeding the obtainedsignal from the sensor into the RFID reader; and integrating atraditional motion sensor, accelerometer, or sensor using ultrasonicwaves into the RFID reader.

Data from the motion sensors can be sent to a processor that may or maynot be part of the RFID reader. Additionally, a range of possiblemovement profiles can be constructed and stored in a memory accessibleby the processor for comparison to the data from the motion sensors. Amovement profile can define a range of sensor data or a sequence ofsensor data that indicate a match condition that the forklift or othervehicle on which the RFID reader is mounted is moving. For example, amatch condition could be as simple as movement in the forward directionfaster than one meter per second for more than a second.

As another example, acceleration of a forklift can be measured by atri-axial accelerometer. The acceleration values can be integrated andfiltered with a low-pass filter to derive the speed and the position ofthe forklift along three axes. Two examples of accelerometer data andderived speed and position data are shown in FIGS. 11A and 11B, wherethe acceleration data for the x-, y-, and z-axes are shown in the topgraph, and the derived velocity and position data are shown in themiddle and bottom graphs, respectively. Using the sensor accelerometerdata and the derived velocity and position information, the system candetermine when the forklift is moving forward or backward faster than 1meter per second over a time span of at least one second. Moreover, thedata measured for three axes can be matched to different movementprofiles including, but not limited to, matching x-axis data todetermine that a forklift is picking up a load, matching z-axis data todetermined that a forklift truck is backing out, and matching y- andz-axis data to determine that the forklift truck is making a turn, forexample a 90 degree turn. The data processor collects and processesmotion sensor data, and once a match condition occurs, the processorgenerates an event to the RFID reader, such as reading a tag in block215 of process 200.

Alternatively, SID can be used to detect an untagged item moving in theantenna read zone of the RFID reader. A SID-based method would beapplicable in a situation where the forklift moves past poles, shelving,or other stationary items in the warehouse or distribution center.Additional processing such as filtering, hysteresis, or heuristics couldbe applied to the SID motion trigger to increase the confidence of thestationary-motion decision.

At decision point 210, the system determines whether the RFID reader isin motion. If it determines (block 210—Yes) that the RFID reader is inmotion, at block 215, an RFID tag in the read zone of the RFID reader isread. At block I, any motion of the tag is detected in the read zonethrough the use of SID. The read zone may be an area in front of or nearthe RFID reader's antenna or antennas where RFID tags may be reliablyinterrogated. Alternatively, the read zone may be narrowed by usingmultiple antennas to determine the distance a tag is from the RFIDreader and only reading tags within a certain distance of the reader.

Motion of RFID tags can be detected by using any of the techniquesdescribed above for measuring distance and angle of the RFID tag, forexample relative to the RFID reader, and determining that a change hasoccurred. Motion of an RFID tag can alternatively be determined bymeasuring the change of the phase angle during an RFID tag response toan RFID reader query. FIGS. 3A and 3B illustrate one example of an RFIDtag motion detection process 300 using phase angle measurements.

When an RFID tag responds to a reader query, the RFID reader hardwarepresents the firmware with a digitized complex signal that has an I(in-phase) component and Q (quadrature) component. Because the valuesfor I and Q may be noisy, multiple adjacent I,Q values in the vicinityof the preamble of the tag response should be used, for example bytaking the root mean square (RMS) value of several adjacent I samples asthe I value and the RMS value of several adjacent Q samples as the Qvalue.

At blocks 302 and 304, the system reads or obtains several adjacent Iand several adjacent Q components from a tag read. Then at blocks 306and 308, the RMS value of the I samples and the RMS value of the Qsamples are calculated. The RMS values of I and Q will be referred to assimply I and Q in the following description for simplicity of notation.The magnitude of the tag response is referred to as received signalstrength indication (RSSI) and is given by the square root of (I²+Q²)The phase angle of the tag response in radians is given by thearctangent of (Q/I).

To determine the phase angle within a 360 degree range, a specificlocation in the preamble of the tag response may be selected, and therelationship of I and Q to zero at that location determined. Thisenables the correct quadrant of the tag response phase angle to beselected, and by determining phase change between quadrants, the systemcan quickly and accurately determine that a tag has moved. However,because the values of I and Q are both subject to random noise, thequadrant may be incorrectly determined for any single I,Q pair. Part ofthe problem can be corrected by ignoring the absolute relationship of Iand Q to zero and using just the relationship of I and Q to each other,that is, whether I and Q have the same sign or different signs.Consequently, the range of the phase angle determination is limited to180 degrees (two quadrants) rather than 360 degrees (four quadrants).The quantities (I+Q)² and (I−Q)² are calculated at blocks 310 and 315.Then by comparing the magnitudes of these quantities, the system candetermine whether I and Q have the same or different signs.

At decision block 320, the system determines if (I+Q)² is greater than(I−Q)². If (I+Q)² is greater than (I−Q)² (block 320—Yes), then I and Qhave the same sign, and at block 330, a positive sign is chosen for thephase angle given by arctan(Q/I). If (I+Q)² is less than (I−Q)² (block320—No), then I and Q have opposite signs, and at block 325 a negativesign is chosen for the phase angle given by arctan(Q/I).

The process continues to decision block 335 from either block 330 orblock 345 where the system determines if a second phase anglemeasurements needs to be measured. A second phase angle measurement isneeded to determine any change in the phase angle in the tag response.If a second phase angle measurement is needed (block 335—Yes), theprocess returns to block 302 to acquire a second set of I and Q pairs.If a second phase angle measurement is not needed (block 335—No), atblock 340 the phase angle change is calculated by subtracting the secondcalculated phase angle from the first calculated phase angle.

Then at decision block 345, the system determines if there has been anychange in the phase angle. If there has been no change in the phaseangle (block 345—No), at block 350 the system concludes that the tag isnot moving, and the process ends at block 399.

If there has been a change in the phase angle (block 345—yes), at block355 the system concludes that the tag is moving. At block 360, thesystem determines the distance the tag moved based upon the calculatedphase angle change, and the process ends at block 399.

The phase angle change is very sensitive to movements of the RFID tagover distance. For example, at a radio frequency of 865 MHz, thewavelength is 347 mm. Thus, the 180 degree range measured is coveredover a travel distance of 173 mm of the tag. Because the phase of theRFID tag response arises from the distance the signal travels, and thedistance is the path from the RFID reader to the tag and back again, thephase will undergo a change through 180 degrees when the distancebetween the reader and the tag changes by 87 mm. For an RFID readeroperating at 915 MHz, a phase change of 180 degrees will occur over areader-to-tag distance change of 82 mm. Consequently, the resolutionwill be slightly better for higher operating frequencies.

Experimentally, repeatability of phase angle measurements showed avariance of about ±5 degrees between a reading at the beginning of thetag response and one at the end of the tag response. Given thisparticular measured variance in phase angle measurement, to determinethat a tag has moved the system may detect a change in phase angle thatexceeds a predetermined error probability. For example, a phase anglechange of 5.625 degrees (180 degrees/32) should be sufficient toindicate that the tag has moved. This is equivalent to a movement of2.71875 mm by the tag directly toward the reader at 865 MHz.

A single dense reader mode (DRM) tag response is 1.8 ms, thus, if theRFID tag were required to move 2.71875 mm during this period of time,for reliable detection of motion the rate of speed should beapproximately 1.5 m/s. A speed of 1.5 m/s may be the slowest speed thata tag might be expected to move in a warehouse environment while aboarda forklift truck. By decreasing the minimum speed to 1 m/s, for amovement of 1.8 mm, the error in phase angle measurement can be reducedto +2 degrees. The variance of the phase angle measurements may bedependent upon many factors including, but not limited to, the strengthof the tag signal and environmental noise. Consequently, the variance inphase angle measurements may be different from the experimentallymeasured value given here.

In testing, the RSSI for the RFID reader used to make the abovemeasurements was strong and above −40 dBm, but the noise floor wasmeasured at −62 dBm. As a result, noise became a significant part of thecomputations. Typical RFID readers have lower noise variances that willallow detection of smaller distances traveled by a tag. Further, if atag responds with FM0 modulation, the response time can be much shorterthan 1.8 ms. Consequently, a lowest speed tag that can be detected withFM0 modulation can be much higher.

One experiment was performed with an Intermec IM5R2 865 MHz RFID readerhaving an unlabeled RF antenna and configured to operate in DRM (densereader mode) such that a queried RFID tag would respond with Millermodulation having an M value of 4. An RFID tag was initially placedthree feet from the reader and then moved away from the readerapproximately one inch at a time. At each position of the tag, thereader was operated for several seconds to obtain several phasereadings. No measurements of phase changes were made while the tag wasin motion. During the experiment, three RFID tags from unknown locationsalso responded to the reader's queries. These three tags had weakersignals of 26 dB, 30 dB, and 34 dB and were used to provide a referenceof statically positioned tags.

The top graph in FIG. 4 shows the phase angle measurements for the threestationary tags. Each tag's phase angle exhibited a tendency to wanderduring the experiment and could be attributed, at least in part, to anuncontrolled environment and movement of the experimenter during thecourse of the experiment. For example, the phase angle measurements forthe tag shown in the middle of the top graph shows that the phase anglechanged in steps as the experimenter stopped the phase measurements tomove the RFID tag being tested. Because the signal strength and thephase angle of the tags change over time, measurements should be takenover as short a time interval as possible.

The bottom graph in FIG. 4 shows the phase angle measurements taken forthe non-stationary tag being tested. The x-axis represents the number ofeach tag read, and the y-axis represents the phase angle. A total of 13measurements were taken; each measurement corresponded to the tag beingmoved from 0 to 12 inches at one inch intervals and starting at adistance of 36 inches from the RFID reader antenna. The one-inchmovements of the tag were made manually and thus were not closelycontrolled during the experiment. At three inches (near x=80) the tagwas barely readable and few readings were obtained, while at 11 inches(near x−240), there were no readings. Multipath signal cancellation frommetallic objects near the reading site could be a contributing factor tothe lack of readings and barely readable tag, but it should be notedthat multipath cancellation is not related to detecting motion of anRFID tag based upon changes in phase angle measurements. At six inches,the phase angle was approximately 90 degrees and wrapped toapproximately −90 degrees. The relatively large swings shown on thegraph for the six inch distance only represent a few degrees ofmovement. The change in phase angle is consistent with the abovepredictions: a rotation through 180 degrees only required a movement ofthe tag of slightly more than three inches. Further, the phase anglemeasurements wander over a range of only a few degrees.

The graphs in FIG. 5 show the variance, in degrees, of the phase anglemeasurements between a measurement taken at the beginning of the tagresponse and one taken at the end of the response. The top graph in FIG.5 shows the phase angle variances for the three stationary tags in thesame order as shown in the top graph for FIG. 4 The signal strength ofthe first tag was 26 dB, the second tag was 34 dB, and the third tag was30 dB. This graph provides a good indication of how 18 dB of noiseaffects the phase determination of signals of varying strength.

The bottom graph in FIG. 5 shows the variance of the phase anglemeasurements for the dynamic tag under test. Note that there is nolonger any clear step motion visible for each position of the tag. Theerror is approximately 4 degrees or less, but can be larger at times.

In FIG. 6, the RSSI of the tag is shown for the non-stationary tag undertest. The RSSI varies periodically between 41 dB and 45 dB. A phaseangle rotation may not cause a large change in magnitude. Because theRSSI variation is periodic, multipath effects could alternately add toand subtract from the main signal. If multipath effects affect the RSSIby such a large amount the phase angle may not be affected to as great aextent. These results show that using RSSI alone to determine tagmovement can be insufficient.

At some distances, the RSSI varied a little, and at many distances, theRSSI varied widely. Although many factors can give rise to this result,one contributor may be the phase angle of the noise. In the IM5R2 RFIDreader used in the experiment, a contributor to noise was the reader'sown reflected carrier wave. The carrier can be reflected by an impedancemismatch between the power amplifiers and the antenna, and the phase ofthe noise can change predictably as the carrier frequency is changed. Atsome frequencies, either I or Q will become highly noisy. The experimentwas conducted at only one frequency, and I and Q were both impaired withbetween 14 dB and 22 dB of noise.

FIG. 7 shows a graph where the measured RSSI is shown on the horizontalaxis, and the corresponding phase angle difference is shown on thevertical axis. The measurements for all four tags are shown. The closestgrouping corresponds to the tag having a response strength of 34 dB.Lower power tags have increasingly larger errors, as expected. Thedynamic tag under test shows larger errors as the signal strength isincreased. Because 45 dB is close to the largest signal that can bemeasured with the equipment used for this experiment, excessive gain cancause the signal to be clipped. Clipped signals will have increasinglydubious magnitudes and phase angles.

Measurement of the change of the phase angle of an RFID tag response canbe implemented not only by one or more microprocessors, but also infirmware for the digital signal processor of an RFID reader.Alternatively, the measurement procedure can be programmed into afield-programmable gate array (FPGA).

Continuing with the process 200 in FIG. 2, at decision point 225, thesystem determines whether the RFID tag is stationary. If the systemdetermines (block 225—Yes) that the tag is stationary within the readzone, at block 230 the tag and corresponding package are considered partof the load being carried by the moving forklift. This information isstored in a database for use by the RFID system in tracking tags andpackages. If the system determines (block 225—No) that the tag is movingwithin the read zone, at block 235 the tag and its package are notconsidered part of the load being carried by the moving forklift. Again,this information can be stored in a database for use by the RFID system.This may happen in the case of reading extraneous tags, perhaps on awarehouse shelf, as the forklift is moving past the shelf. Thus, theextraneous tag and package may safely be excluded from the forkliftload.

Whether the tag is considered part of the load at block 230 or not partof the load at block 235, the process returns to block 205 where themotion sensor again detects motion of the RFID reader.

If the system determines (block 210—No) that the RFID reader is not inmotion, at block 240, an RFID tag in the read zone of the RFID reader isread. At block 245, any motion of the tag is detected in the read zonethrough the use of SID.

At decision point 250, the system determines whether the tag was inmotion within the read zone and then became stationary within the readzone. If it determines (block 250—Yes) that the RFID tag moved and thenbecame stationary within the read zone, then at block 255, a distancemeasurement between the tag and the RFID reader is made. A distancemeasurement may be made by employing SID-based techniques where thebackground noise detected by the RFID reader changes as the localenvironment of the mobile RFID reader changes. For example, an RFIDreader mounted on a mobile forklift may detect different backgroundnoise when moving between shelves packed with tagged packages or whentraveling down a more open main aisle in the warehouse.

At decision point 260, if the tag is within a certain distance of theRFID reader, for example, the distance is within the load space of theforklift, then at block 265, the tag and the package to which the tag isattached are considered as having been added to the load space.

If the system determines (block 260—No) that the tag is not within theload space, at block 235 the tag and package are not considered part ofthe load. This information can be stored in a database for use by theRFID system.

If the system determines (block 250—No) that the tag did not move andthen become stationary within the read zone, then at decision point 270,it determines whether the tag was stationary within the read zone andthen moved out of the read zone. If the system determines (block270—Yes) that the tag was stationary within the read zone and then movedoutside of the read zone, at block 275, the tag and correspondingpackage may be classified as either having been removed from the load,or the tag and package fell off of the forklift. This information can bestored in a database for use by the RFID system. However, if the systemdetermines (block 270—No) that the tag was not stationary within theread zone and then moved outside of the read zone, at block 280 the tagis considered an extraneous tag and ignored. This case may arise if theRFID reader responds to stray RF reflections or RF noise.

In all of the above scenarios for the motion sensor detection process200, after a tag has been classified as being part of a load (block230), not part of a load (block 235), added to a load (block 260),removed from a load (block 275), or an extraneous tag (block 280), theprocess returns to block 205 where the motion sensor detects motion ofthe RFID reader again.

Both the volume sensor detection process 100 and the motion sensordetection process 200, may be adapted to accommodate the RFID system.For example, depending upon the speed of the forklift and/or the speedof processing RFID and SID information, multiple tags may be read andprocessed in each block that reads or processes an RFID tag. Thus, inthe volume sensor detection process 100, multiple tags may be read andcompared to a movement of the forklift, and in the motion sensordetection process 200, multiple tags may be read and their motion may bemonitored to determine if the tags are moving or stationary within theread zone before re-detecting motion of the RFID reader again.

FIGS. 8A and 9A show example block diagrams 800, 900 of a mobile RFIDsystem 810, 910 used to read one or more packages with RFID tags 850,950. With RFID system 810 in FIG. 8, a motion sensor 835 sends datadirectly to the RFID reader 830 for processing by the reader, while withRFID system 910 in FIG. 9, the motion sensor 935 sends data directly tothe mobile computer 920 for processing. For the RFID system in FIG. 8,in one configuration if the RFID reader and the sensor 835 are mountedon the back rest of the load, then a sufficiently sensitive sensor candetect motion of the fork moving up and down. For the RFID system inFIG. 9, in one configuration, if the sensor and the computer are mountedin the body of the forklift truck, only motion of the forklift truckcould be detectable. The RFID system 810 in FIG. 8 includes a mobilecomputer 820, an RFID reader 830, a motion sensor 835, and one or moreRF antennas 840. Similarly, the RFID system 910 in FIG. 9 includes amobile computer 920, an RFID reader 930, a motion sensor 935, and one ormore RF antennas 940.

Note that FIGS. 8 and 9 and the associated discussions provide a brief,general description of a suitable computing environment in which theinvention can be implemented. Although not required, aspects of theinvention are described in the general context of computer-executableinstructions, such as routines executed by a general-purpose computer,e.g., stationary and mobile computers. Those skilled in the relevant artwill appreciate that the invention can be practiced with othercommunications, data processing, or computer system configurations,including: Internet appliances, hand-held devices (including personaldigital assistants (PDAs)), wearable computers, all manner of cellularor mobile phones, multi-processor systems, microprocessor-based orprogrammable consumer electronics, set-top boxes, network PCs,mini-computers, mainframe computers, server computers, and the like.Indeed, the terms “computer” and the like are generally usedinterchangeably herein, and refer to any of the above devices andsystems, as well as any data processor.

Aspects of the invention can be embodied in a special purpose computeror data processor that is specifically programmed, configured, orconstructed to perform one or more of the computer-executableinstructions explained in detail herein. Aspects of the invention canalso be practiced in distributed computing environments where tasks ormodules are performed by remote processing devices, which are linkedthrough a communications network, such as a Local Area Network (LAN),Wide Area Network (WAN), or the Internet. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices. For example, the computer 820, 920 may becoupled via a network to other computers (not shown).

Aspects of the invention may be stored or distributed oncomputer-readable media, including magnetically or optically readablecomputer discs, hard-wired or preprogrammed chips (e.g., EEPROMsemiconductor chips), nanotechnology memory, biological memory, or otherdata storage media. Indeed, computer implemented instructions, datastructures, screen displays, and other data under aspects of theinvention may be distributed over the Internet or over other networks(including wireless networks), on a propagated signal on a propagationmedium (e.g., an electromagnetic wave(s), a sound wave, etc.) over aperiod of time, or they may be provided on any analog or digital network(packet switched, circuit switched, or other scheme).

As shown in FIG. 10, the mobile computer 820, 920 includes a processor1021 that may be used to run RFID reader applications that may be storedin the memory units 1022 and may process the RFID information and thespatial and/or motion information; memory units 1022 may include but arenot limited to, RAM, ROM, and any combination of volatile andnon-volatile memory; a database 1023 may be used for storing RFIDinformation and/or customer order lists, where the database 1023 may bestored in the memory units 1022; and a network interface 1024 thatenables information to be sent over a network such as RFID taginformation and order lists. Examples of a network interface 1024include, but are not limited to, modems such as cable, ADSL, or optical,interfaces that communicate through wireless frequencies or infraredfrequencies, and network interface cards. Of course, the computer 820,920 may include other elements (not shown), including input or outputelements such as a printer, plotter, audio speakers, tactile orolfactory output devices, network connection, wireless transceiver,keyboard, pointing device (e.g. mouse), microphone, joystick, pen, gamepad, scanner, digital camera, video camera, etc.

Locations at which the computer 820, 920 may reside include, but are notlimited to, within an RFID reader on a forklift, at a mobile site, suchas a handheld device carried by a warehouse worker, and at a remote sitewhich may or may not be within the warehouse.

The RFID reader 830, 930 includes standard components for communicationwith RFID tags including one or more antennas 840, 940 for receiving andtransmitting RF signals. The RFID reader 830, 930 can include a spatialsensor that senses items within a defined volume or area. Alternativelyor additionally, the RFID reader 830, 930 can include a sensor forsensing motion of RFID tags. The RFID reader 830 in FIG. 8 includes aprocessor that can receive and process data from the motion sensor 835.

The motion sensor 835, 935 senses motion of the RFID reader 830, 930 andmay be mounted on a mobile forklift so when the forklift moves, the RFIDreader 830, 930 also moves. The sensor 835 may be integrated into theRFID reader 830 or be an independent unit in some embodiments.

The RFID tags 850, 950 may be attached to packages or other items ordevices. A large number of tags may be located near each other and alsoaround the warehouse or distribution center. The tags and packages maybe in transit for many reasons including being carried by a forklift orperson, being added to a forklift load, being removed from a forkliftload, and falling off of a forklift. The RFID tags 850, 950 andcorresponding packages may also be stationary in various locations suchas on a stationary forklift, on a shelf, and in a queue waiting to beloaded onto a forklift. If an RFID tag 850, 950 is within the read zoneof an RFID reader 830, 930, the RFID reader 830, 930 will be able toidentify the tag and its location, unless the tag is an extraneous tag.In that case, the above described motion sensor detection process 200that utilizes motion and spatial information may be able to accuratelydetermine whether an identified RFID tag is an extraneous tag.

The words “herein,” “above,” “below,” and words of similar import, whenused in this application, shall refer to this application as a whole andnot to any particular portions of this application. Where the contextpermits, words in the above Detailed Description using the singular orplural number may also include the plural or singular numberrespectively. The word “or,” in reference to a list of two or moreitems, covers all of the following interpretations of the word: any ofthe items in the list, all of the items in the list, and any combinationof the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whilean RFID reader for reading RFID tags are mentioned, any readingapparatus for reading devices emitting radio-frequency signals may beused under the principles disclosed herein.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While the above description describes certain embodiments of theinvention, and describes the best mode contemplated, no matter howdetailed the above appears in text, the invention can be practiced inmany ways. Details of the system may vary considerably in itsimplementation details, while still being encompassed by the inventiondisclosed herein. As noted above, particular terminology used whendescribing certain features or aspects of the invention should not betaken to imply that the terminology is being redefined herein to berestricted to any specific characteristics, features, or aspects of theinvention with which that terminology is associated. In general, theterms used in the following claims should not be construed to limit theinvention to the specific embodiments disclosed in the specification,unless the above Detailed Description section explicitly defines suchterms. Accordingly, the actual scope of the invention encompasses notonly the disclosed embodiments, but also all equivalent ways ofpracticing or implementing the invention under the claims.

1. A system for identifying a radio frequency identification (RFID) tagwithin a defined zone, comprising: an RFID reader configured to scan foran RFID tag within a read zone of the RFID reader, wherein the read zoneat least partially overlaps with the defined zone, and wherein thedefined zone is at a location near one or more antennas of the RFIDreader; a sensor component configured to provide data to at least assistin determining positional data of the RFID tag relative to the RFIDreader; a database storing the positional data and limits of the definedzone; and, a processor communicatively coupled to the RFID reader, thesensor component, and the database, wherein the processor is configuredto compare the positional data from the sensor component with thedefined zone limits to determine whether the RFID tag is within thedefined zone, and store the determination in the database.
 2. The systemof claim 1 wherein the RFID reader is secured or removably secured to avehicle, and wherein the read zone is movable with respect to thevehicle.
 3. The system of claim 1 wherein the sensor component is anaccelerometer or gyroscope.
 4. The system of claim 1 wherein the definedzone is a load space of a forklift truck, and wherein the sensorcomponent is configured to determine a position of the RFID tag.
 5. Thesystem of claim 1 wherein the sensor component uses spatialidentification technology.
 6. The system of claim 1 wherein the sensorcomponent includes two or more RF antennas that have a known separationfor determining a location of the RFID tag.
 7. The system of claim 1wherein the sensor component includes logic for determining a distancebetween the RFID reader and the RFID tag based upon a received signalstrength.
 8. The system of claim 1 wherein the processor is furtherconfigured to determine a phase between received signals from the RFIDtag and to determine whether the RFID tag is in motion relative to theRFID reader based on a change in phase.
 9. The system of claim 1 whereinthe processor is further configured to determine whether the RFID tag isin motion relative to the RFID reader based on backscatter modulation.10. A system for identifying an RFID tag within a movable load space,comprising: an RFID reader configured: to scan for an RFID tag within aread zone of the RFID reader and to determine a distance and an anglebetween the RFID reader and the RFID tag, wherein the read zone at leastpartially overlaps with the movable load space, and the movable loadspace is near the RFID reader; a data store storing the distance and theangle and limits of the movable load space; a processor communicativelycoupled to the RFID reader and the data store, wherein the processor isconfigured to: compare the distance and the angle between the RFIDreader and the RFID tag with the load space limits to determine whetherthe RFID tag is within the movable load space; and store thedetermination in the database.
 11. The system of claim 10 wherein theload space moves with a forklift truck, and further wherein the RFIDreader is secured or removably secured to the forklift truck.
 12. Thesystem of claim 10 wherein determining a distance and an angle betweenthe RFID reader and the RFID tag comprises using wireless backscattermodulation.
 13. The system of claim 10 wherein determining a distanceand an angle between the RFID reader and the RFID tag comprises usingmultiple RF antennas having known separations to triangulate a positionof the RFID tag.
 14. The system of claim 10 wherein determining adistance and an angle between the RFID reader and the RFID tag comprisesusing received signal strength and logic to determine a distance betweenthe RFID reader and the RFID tag.
 15. A system for identifying an RFIDtag within a defined zone, comprising: an RFID reader configured to readan RFID tag; means, coupled to the RFID reader, for determiningpositional data of the RFID tag; and, means, coupled to the means fordetermining positional data, for determining whether the RFID tag iswithin a defined space based at least in part on the positional datadetermined from the means for determining positional data.
 16. A systemfor distinguishing an RFID tag within a movable load space from at leastone extraneous tag, the system comprising: an RFID tag detectorconfigured to scan for a first RFID tag within a detection zone of theRFID detector, wherein the detection zone at least partially overlapswith the load space; a first sensor configured to monitor movement ofthe RFID detector; a second sensor configured to monitor movement of thefirst RFID tag; a processor communicatively coupled to the RFIDdetector, the first sensor, and the second sensor, wherein the processoris configured to compare movement of the first RFID tag relative tomovement of the RFID detector, and, determine whether the first RFID tagis in the load space, is not in the load space, has been added to theload space, has been removed from the load space, or is an extraneoustag based upon the movement of the first RFID tag within the read zone.17. The system of claim 16 wherein the load space moves with a forklifttruck, and further wherein the RFID reader is secured or removablysecured to the forklift truck.
 18. The system of claim 16 wherein thefirst sensor receives a signal from a speedometer or other instrument ofa vehicle carrying the load.
 19. The system of claim 17 wherein thefirst sensor is configured to detect a predetermined movement profilecorresponding to movement of the forklift truck.
 20. The system of claim16 wherein the second sensor uses spatial identification technology. 21.The system of claim 16 wherein the second sensor uses wirelessbackscatter modulation.
 22. The system of claim 16 wherein the secondsensor uses phase angle measurements.
 23. A method of identifying anRFID tag within a movable and defined zone, the method comprising:determining a position of the RFID tag; comparing limits of the definedzone with the determined position of the RFID tag, wherein the definedzone moves relative to a set location; and, determining whether the RFIDtag is within the defined zone.
 24. The system of claim 23 whereindetermining a position of the RFID tag comprises using spatialidentification technology.
 25. The system of claim 23 whereindetermining a position of the RFID tag comprises using backscattermodulation.
 26. A method of distinguishing an RFID tag within a loadfrom an extraneous tag, comprising: monitoring movement of an RFIDreader; reading a first RFID tag; monitoring movement of the first RFIDtag within a read zone of the RFID reader; and, determining whether thefirst RFID tag is part of the load, is not part of the load, has beenadded to the load, has been removed from the load, or is an extraneoustag based upon movement of the first RFID tag within the read zone. 27.The method of claim 26, further comprising performing a measurement of adistance between the RFID tag and the RFID reader.
 28. The method ofclaim 26 wherein monitoring movement of the first RFID tag comprisesmeasuring a phase angle change of a response of the first RFID tag. 29.The method of claim 26 wherein monitoring movement of an RFID readercomprises detecting a predetermined movement profile of the RFID reader.30. A tangible computer-readable medium storing processing instructionsfor implementing an operation performed by a computer, the operationcomprising: monitoring movement of an RFID reader; reading a first RFIDtag; monitoring movement of the first RFID tag within a read zone of theRFID reader; and, determining whether the first RFID tag is part of theload, is not part of the load, has been added to the load, has beenremoved from the load, or is an extraneous tag based upon movement ofthe first RFID tag within the read zone.
 31. The tangiblecomputer-readable medium of claim 30, wherein the operation furthercomprises performing a measurement of a distance between the RFID tagand the RFID reader.